Compressor inter-stage temperature control

ABSTRACT

A method, system and apparatus for providing temperature control of compressed gases between stages of a multiple-stage compressor, by selectively manipulating a valve which can cause at least a portion of the compressed gases to flow through an air-cooled heat exchanger.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of the filing of U.S. Provisional Patent Application Ser. No. 61/476,099, entitled “Compressor Inter-Stage Temperature Control”, filed on Apr. 15, 2011, and the specification thereof is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention (Technical Field)

Embodiments of the present invention relate to a method, system, and apparatus for providing inter-stage temperature control of a compressor, particularly at least partially via the use of an air cooler.

2. Description of Related Art

One of the major problems encountered with known vapor recovery systems is condensation of the vapors in the air-cooled compressor, which compressor is used to raise the pressure of the recovered vapors to the pressure of the sales line. In known systems, some of the recovered vapors are at liquid phase at the typical sales line pressures, but change to a vapor phase when the sales line pressure is reduced to the atmospheric pressure of the storage tank. Known systems prevent the recovered vapors from going back to the liquid phase during the compression cycle by maintaining, through all stages of compression, the temperature of the recovered vapors above the hydrocarbon dew-point of the recovered vapors. In order to control, during the compression cycle, the temperature of the recovered vapors the air cooler is removed from the compressor and is replaced by a system that utilizes the recovered liquids instead of the atmosphere as a heat sink.

Failure to adequately maintain proper temperature of gasses between stages of compression can result in recycle loops being formed. There is thus a need for a method, apparatus, and system of vapor recovery that can be used in temperate climates and will prevent the formation of recycle loops, be simple to install on an existing compressor setup, or incorporated into the design of a new vapor recovery unit and which uses ambient air to cool one or more portions of the system.

Objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawing, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.

BRIEF SUMMARY OF EMBODIMENTS OF THE PRESENT INVENTION

An embodiment of the present invention relates to a method for regulating temperature of a gas between stages of compression which includes providing a control valve between stages of compression; providing an air-cooled heat exchanger; monitoring the temperature of the gas in at least one location; and manipulating the control valve such that at least a portion of compressed gas from a first stage of compression can be selectively caused to flow through the air-cooled heat exchanger before being introduced into a second stage of compression. The at least one location can be downstream of an outlet of the second stage of compression. The at least one location can be between an outlet of the air-cooled heat exchanger and an inlet of the control valve. Manipulating the control valve can include modulating the control valve.

In one embodiment, the control valve can include a first inlet which is coupled to an outlet of the first stage of compression, the control valve can include a second inlet which is coupled to an outlet of the air-cooled heat exchanger, and/or manipulating the control valve can include adjusting a flow ratio, the ratio being a formed between a flow rate of gas entering the first inlet of the control valve and a flow rate of gas entering the second inlet of the control valve.

In one embodiment, manipulating the control valve can include modulating the control valve with a modulating valve, and the modulating valve can optionally be controlled in response to a temperature monitored in a second location and the control valve can be adjusted in response to a combination of the temperature that is monitored at the first location and a temperature that is monitored at the second location. The first location can include a location that is downstream of the second stage of compression and the second location can include a location between an outlet of the air-cooled heat exchanger and the second inlet of the control valve.

Optionally, the control valve can be manipulated so as to maintain a temperature of the gas after having passed through the second stage of compression within a predetermined temperature range and/or to maintain a temperature of gas exiting the air-cooled heat exchanger above a predetermined set point. In one embodiment, the second stage of compression is a third stage of compression of a multi-stage compressor and the first stage of compression is a second stage of compression of the multi-stage compressor. Optionally, the control valve can include an outlet that is communicably coupled to an inter-stage scrubber.

An embodiment of the present invention also relates to an apparatus for controlling temperature of gases between stages of compression for a multi-stage compressor which includes a control valve having first and second inlets and an outlet, the first inlet coupled to an outlet of a first stage of the multi-stage compressor, the second inlet coupled to an outlet of an air-cooled heat exchanger, and the outlet of the control valve coupled to an inter-stage scrubber; and a modulating valve communicably coupled to the control valve; the modulating valve configured to manipulate the control valve based on a temperature of the gases at a location between an outlet of the air-cooled heat exchanger and the second inlet of the control valve. In one embodiment, the control valve can be manipulated based on a temperature of the gases at a location that is downstream from a second stage of the multi-stage compressor. Optionally, process control logic can be connected to the modulating valve. The control valve preferably adjusts a mixture of gas having passed through the air-cooled heat exchanger with hot gas exiting the first stage of the multi-stage compressor.

In one embodiment, the control valve and the air-cooled heat exchanger are positioned such that at least a portion of hot gas from the first stage of compression can be caused to flow through the air-cooled heat exchanger before entering the second inlet of the control valve and at least a portion of hot gas from the first stage of compression of the multi-stage compressor enters the second inlet of the control valve.

In one embodiment, each of the components are duplicated and placed on another inter-stage of compression such that, rather than being disposed between the first and second stages of compression of the multi-stage compressor, the duplicated components are instead disposed between second and third stages of the multi-stage compressor.

Objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The accompanying drawing, which is incorporated into and forms a part of the specification, illustrates one or more embodiments of the present invention and, together with the description, serves to explain the principles of the invention. The drawing is only for the purpose of illustrating one or more embodiments of the invention and is not to be construed as limiting the invention. FIG. 1 is a flow diagram illustrating an embodiment of the present invention as applied to a two-stage compressor.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention is directed to a method, system, and apparatus for vapor processing that utilizes a compressor equipped with an air cooler. Embodiments of the present invention can be used in conjunction with a new compressor, can be incorporated into the design of a compressor, or can be retrofitted to an already-installed compressor system.

In one embodiment, for a multi-stage compressor, an air cooled compressor can be equipped with temperature control valves on each stage of compression. The temperature control valves can be controlled by a thermostat installed in the piping downstream of the compression stage that is being controlled. The temperature control valves preferably mix a portion of the hot gas of compression with a portion of the cool gas from the air cooler to provide a gas temperature at each stage of compression that is high enough to prevent or inhibit the formation of recycle loops. This can be done by monitoring a temperature of the compressed gas and adjusting the one or more valves such that a greater or lesser amount of the compressed gas is caused to flow through an air-cooled heat exchanger. In one embodiment wherein multiple inter-stages of compression exist and wherein a control valve is provided for each of the multiple inter-stages of compression, the valve for each inter-stage of compression preferably acts independently of the other inter-stages. Thus, each valve can have two inlets such that hot gas directly from a stage of compression enters in one inlet and cooled compressed gas from an air-cooled heat exchanger enters at a second inlet and the valve is manipulated to adjust the ratio there between. Optionally, the one or more control valves can be adjusted based on sensed temperatures in relation to one or more predetermined temperature set-points. In one embodiment, a desired temperature set-point can be established and the valve can continuously and/or periodically adjust the mix ration in order to maintain that set-point or within a margin of error of that set point.

In one embodiment, for a two stage compressor, one temperature control valve can optionally be used. In one embodiment, for a three stage compressor, two temperature control valves can be used. In one embodiment for multiple stage compressors, one temperature control valve less than the number of stages of compression can be used.

The term “PICT valve” and/or “process inter-stage controlled temperature” is used throughout this application to mean a temperature control valve or any other mechanism, system, assembly, circuit, sensor, combination thereof, or the like, which can be used in place of a temperature control valve and which will perform substantially the same operation.

In one embodiment, because the PICT valve can be made to divert only a portion of the hot compressed gas to a 1^(st) stage cooler, the volume of gas flowing through the cooler is thus less than if all of the hot compressed gas were directed therethrough. Because comparatively less gas is flowing through the 1^(st) stage cooler, the cooling coil is thus comparatively over-sized. Therefore, the gas flowing through the cooling coil is cooled more than would be the case if all of the hot compressed gases were directed therethrough. The gas flowing through the cooling coil is subject to hydrate formation, so the temperature of the gas flowing through the cooling coil is preferably maintained above the gas hydrate formation temperature. This can be accomplished by monitoring the temperature of the gas exiting the cooler and adjusting the PICT valve in response to predetermined temperature parameters.

To maintain the temperature of the gas flowing through the cooling coil to a temperature above hydrate formation, a thermocouple, transducer, or other sensor, method, system, circuit, apparatus, or combination thereof is optionally installed in the piping downstream of the cooling coil outlet. The sensor preferably monitors the temperature of the gas exiting the cooling coil. As long as the gas exiting the cooling coil is above the hydrate formation temperature of the gas, the thermostat downstream of the compression stage preferably controls the operation of the PICT valve.

If the ambient temperature becomes low enough to cause the temperature of the gas exiting the cooling coil to approach hydrate formation temperature, the transducer through a process logic control unit (“PLC”) preferably overrides the thermostat and the PLC takes control of the PICT valve and sends more hot compressed gas through the cooling coil. Of course other circuits, and control mechanisms can be used in place of the transducer and PLC to effect the same actions. As long as the ambient temperature is low enough to create a potential problem with hydrate formation in the cooling coil, the transducer and PLC can control the PICT valve to maintain the gas temperature in the cooling coil above hydrate formation temperature.

During the times that the PLC is controlling the PICT valve, some condensation of the recovered vapors can occur. The amount of condensation that can occur, though, is much less than the amount of condensation that would occur, under the same ambient temperature conditions, on an uncontrolled compressor, and the small amount of condensation that can occur is not enough to affect the vapor recovery process.

In one embodiment, the PICT valve can be designed for use in the piping connecting the compression stages of a compressor, the design of the valve can optionally be specialized. For example, the valve can be powered by a motor system, or formed from another non-diaphragm mechanism. In one embodiment, the PICT valve preferably has as low of a pressure drop as practical. In one embodiment, the PICT valve can optionally incorporate a diaphragm opposed by a spring. The movement of the diaphragm can optionally be controlled by a gas signal from a temperature control device. In one embodiment, the PICT valve does not shut off the flow of gas, movement of the diaphragm does not change the flow capacity of the PICT valve, and completely closing either the cool or hot port does not change the flow capacity of the PICT valve because each port is capable of providing the full flow capacity of the of the compressor through PICT valve.

Referring now to FIG. 1 a flow diagram of the present invention as applied to a two-stage compressor is illustrated. Gas flow line 1 preferably moves the vapors to be compressed into the inlet scrubber 2. Liquid level control 3 and dump valve 4 are preferably installed in inlet scrubber 2. Tubing line 5 preferably sends an output signal from liquid level control 3 to motor valve 4. Liquid flow line 6 preferably sends the liquids separated by inlet scrubber 2 to point 7. Gas flow line 8 preferably moves the vapors from inlet scrubber 2 to the suction port 44 of first stage of compression 9. First stage of compression 9 preferably discharges through discharge port 45. Flow line 10 preferably moves the hot compressed vapors from discharge port 45 of first stage of compression 9 to point 11. Gas flow line 12 preferably moves at least a portion of the hot compressed vapors from point 11 to inlet 13 of first stage gas cooler 14.

First stage gas cooler 14 is preferably cooled by force draft air driven by fan 15. Fan 15 is driven by the compressor power source, which can optionally include, but is not limited to an engine, an electric motor, a pneumatic motor, a hydraulic motor, combinations thereof, and the like (note that the compressor power source is not illustrate in FIG. 1). The hot compressed vapors preferably flow through the radiator type air cooling section of first stage air cooler 14 and exit at outlet 16 of first stage air cooler 14. Gas flow line 17 preferably moves the cooled compressed vapors from outlet 16 of gas cooler 14 to cool port 18 of PICT valve 19.

In one embodiment, PICT valve 19 comprises a three-way gas temperature control valve. Gas flow line 20 preferably moves hot compressed vapors from point 11 to hot port 21 of PICT valve 19. Port 22 is the common port of PICT valve 19. Flow line 23 is a flow line that carries the temperature controlled, compressed vapors to inter stage scrubber 24. Flow line 25 preferably carries the temperature controlled, compressed vapors to the inlet port 26 of second stage of compression 27. Second stage of compression 27 preferably discharges through discharge port 28. Flow line 29 preferably carries the hot compressed vapors from second stage of compression 27 to either be further controlled by another PICT valve for temperature control of a third stage of compression or else to the discharge of the compressor. Thermostat 30 preferably senses the temperature of the vapors being carried in flow line 29. Thermostat 30 preferably increases output pressure to increase the temperature of the vapors flowing in line 29. Tubing line 47 preferably carries supply gas to thermostat 30. Line 31 is a tubing line that carries the output signal of thermostat 30 to modulating control valve 38, the modulating control valve 38 preferably receives an electrical signal from PLC 32. Line 39 is a tubing line that carries the pneumatic control pressure signal to the diaphragm of PICT valve 19. Temperature transmitter 33 is a temperature transducer. Line 34 is an electrical line that connects transducer 33 to PLC 32. Line 36 is an electrical line that connects PLC 32 to modulating control valve 38.

In operation, the vapors in line 1 enter inlet scrubber 2. Inlet scrubber 2 removes any free liquids contained in the vapors. The free liquids fall to the bottom of inlet scrubber 2 and, when a fluid level is sensed by liquid level controller 3, a pneumatic signal is sent to motor valve 4. The pneumatic signal opens motor valve 4 causing excess liquids to be dumped through motor valve 4 and line 6 to point 7. (The flow of the liquids will be further described).

The liquid free vapors exit inlet scrubber 2 and flow through line 8 to the suction port 44 of first stage of compression 9. First stage of compression 9 increases the pressure and temperature of the vapors. The hot compressed vapors exit first stage of compression 9 at discharge port 45 and flow through line 10 to point 11. At point 11 the volume of vapors being carried in line 10 can split into two proportions. One of the proportions of the vapors can flow through line 12, to the inlet 13 of first stage gas cooler 14, and through cooler 14, outlet 16, and line 17 to the cool port 18 of PICT valve 19. The other proportion of the volume of vapors being carried in flow line 10 can flow from point 11 through flow line 20 to the hot port 21 of PICT valve 19. PICT valve 19 preferably controls the volume of gas flowing through flow lines 12 and 20. Depending upon the temperature requirement of the discharged gas from second stage of compression 27, all or none of the volume of gas in flow line 10 can flow through either flow line 12 or flow line 20 to common port 22 of PICT valve 19.

In one embodiment, the temperature controlled vapors from first stage of compression 9 can flow from common port 22 of PICT valve 19 through flow line 23 into inter stage scrubber 24. In inter stage scrubber 24 any free liquids can be removed from the vapors. The free liquids preferably fall to the bottom of inter stage scrubber 24. When liquid level controller 40 senses a liquid level in inter stage scrubber 24 it can optionally send a signal, which can be pneumatic or electrical, through line 46 to motor valve 41. The signal preferably opens motor valve 41 to dump the liquids through line 42 to point 7. At point 7 the liquids from inlet scrubber 2 and inter stage scrubber 24 preferably join and flow through line 43 for further processing or storage. In one embodiment, the temperature controlled vapors preferably flow from inner stage scrubber 24 through flow line 25 to suction port 26 of second stage of compression 27. Second stage of compression 27 preferably increases the pressure and temperature of the vapors.

The vapors can exit second stage of compression 27 through discharge port 28 into flow line 29. Thermostat 30 senses the temperature of the gas in flow line 29 and pneumatically controls the positioning of PICT valve 19 to maintain a set discharge temperature. Thermostat 30 is preferably set to maintain the discharge temperature above the dew-point temperature of the vapors being compressed. Depending upon the composition of the vapors and the amount of compression, the dew-point temperature of the vapors can vary widely. On a three-stage compressor a discharge temperature of about 200 to about 280 degrees Fahrenheit is typically high enough to be above the dew-point of the vapors.

When ambient temperatures decrease to a point where the temperature of the gas exiting gas cooler 14 approaches gas hydrate temperature (hydrate temperature depends on the composition and pressure of the gas), temperature transducer 33 preferably sends through line 34 an electrical signal to activate PLC 32 (the hydrate temperature at which PLC 32 will activate is preferably predetermined and pre-set). When PLC 32 is activated it preferably sends an electrical signal to modulating valve 38, which can optionally include an electro-pneumatic modulating valve, to begin controlling PICT valve 19 to send more hot gas through air cooler 14. As long as the ambient temperature is low enough to cause possible gas hydrating in gas cooler 14, PLC 32 and modulating control valve 38 will preferably continue controlling PICT valve 19. As soon as the ambient temperature increases and the gas temperature exiting gas cooler 14 increases approximately five degrees above the gas hydrate temperature, PLC 32 opens modulating control valve 38 and thermostat 30 again takes over control of PICT valve 19.

Although the foregoing description made reference to such things as transducers, pressure signals, motor valves, and a PLC, other components and configurations can be used in place thereof. For example, one or more sensors can be used in place of the transducers, the use of a pressure signal can be replaced by electrical, pneumatic, hydraulic, and hydraulic lines, and/or a combination thereof. Optionally, a pressure signal can also optionally be replaced with a mechanical linkage. Motor valves, can be replaced with mechanical valves, including valves operated via a mechanical linkage. The PLC can optionally be replaced with pneumatic logic, a microcontroller, a microprocessor, an electrical circuit, a mechanical logic device, a computer, combinations thereof, and the like.

In one embodiment, modulating control valve 38 is not provided. In this embodiment, one or more sensors and/or transducers are connected to an electrical, pneumatic or other type of circuit that monitors temperature and adjusts PICT valve 19. For example, PICT valve 19 can be electrically controlled and can be adjusted from a circuit, such as PLC 32, which circuit preferably monitors thermostat 30 and transducer 33 and which adjusts valve 19 in response to predetermined temperature set points or temperature ranges.

Although the invention has been described in detail with particular reference to these preferred embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents. The entire disclosures of all references, applications, patents, and publications cited above are hereby incorporated by reference. 

1. A method for regulating temperature of a gas between stages of compression comprising: providing a control valve between stages of compression; providing an air-cooled heat exchanger; monitoring the temperature of the gas in at least one location; and manipulating the control valve such that at least a portion of compressed gas from a first stage of compression can be selectively caused to flow through the air-cooled heat exchanger before being introduced into a second stage of compression.
 2. The method of claim 1 wherein the at least one location is downstream of an outlet of the second stage of compression.
 3. The method of claim 1 wherein the at least one location is between an outlet of the air-cooled heat exchanger and an inlet of the control valve.
 4. The method of claim 1 wherein manipulating the control valve comprises modulating the control valve.
 5. The method of claim 1 wherein the control valve comprises a first inlet which is coupled to an outlet of the first stage of compression.
 6. The method of claim 5 wherein the control valve comprises a second inlet which is coupled to an outlet of the air-cooled heat exchanger.
 7. The method of claim 6 wherein manipulating the control valve comprises adjusting a flow ratio, the ratio being a formed between a flow rate of gas entering the first inlet of the control valve and a flow rate of gas entering the second inlet of the control valve.
 8. The method of claim 7 wherein manipulating the control valve further comprises modulating the control valve with a modulating valve.
 9. The method of claim 8 wherein the modulating valve is controlled in response to a temperature monitored in a second location and wherein the control valve is adjusted in response to a combination of the temperature that is monitored at the first location and a temperature that is monitored at the second location.
 10. The method of claim 9 wherein the first location comprises a location that is downstream of the second stage of compression and wherein the second location comprises a location between an outlet of the air-cooled heat exchanger and the second inlet of the control valve.
 11. The method of claim 1 wherein the control valve is manipulated so as to maintain a temperature of the gas after having passed through the second stage of compression within a predetermined temperature range.
 12. The method of claim 1 wherein the control valve is manipulated so as to maintain a temperature of gas exiting the air-cooled heat exchanger above a predetermined set point.
 13. The method of claim 1 wherein the second stage of compression comprises a third stage of compression of a multi-stage compressor and wherein the first stage of compression comprises a second stage of compression of the multi-stage compressor.
 14. The method of claim 1 wherein the control valve comprises an outlet communicably coupled to an inter-stage scrubber.
 15. An apparatus for controlling temperature of gases between stages of compression for a multi-stage compressor comprising: a control valve, said control valve comprising first and second inlets and an outlet, said first inlet coupled to an outlet of a first stage of the multi-stage compressor, said second inlet coupled to an outlet of an air-cooled heat exchanger, said outlet of said control valve coupled to an inter-stage scrubber; and a modulating valve communicably coupled to said control valve; said modulating valve configured to manipulate said control valve based on a temperature of the gases at a location between an outlet of said air-cooled heat exchanger and said second inlet of said control valve.
 16. The apparatus of claim 15 wherein said control valve is manipulated based on a temperature of the gases at a location that is downstream from a second stage of the multi-stage compressor.
 17. The apparatus of claim 15 further comprising process control logic connected to said modulating valve.
 18. The apparatus of claim 15 wherein said control valve adjusts a mixture of gas having passed through said air-cooled heat exchanger with hot gas exiting the first stage of the multi-stage compressor.
 19. The apparatus of claim 15 wherein said control valve and said air-cooled heat exchanger are positioned such that at least a portion of hot gas from the first stage of compression can be caused to flow through said air-cooled heat exchanger before entering said second inlet of said control valve and at least a portion of hot gas from the first stage of compression of the multi-stage compressor enters said second inlet of said control valve.
 20. The apparatus of claim 15 wherein each of said components are duplicated and rather than being disposed between the first and second stages of compression of the multi-stage compressor, the duplicated components are instead disposed between second and third stages of the multi-stage compressor. 